This invention relates to a paper detecting apparatus for a printer for detecting paper which passes a paper transport path of the printer.
In conventional printers, various timings such as a timing of printing are controlled in response to passage of paper, and to this end, it is necessary to detect presence or absence of paper or an end of paper which passes a paper transport path. Such detection of paper requires paper detecting means for detecting paper in a paper transport path, means for transmitting a result of detection of the paper detecting means to a controlling section, and so forth.
A paper detecting apparatus for a printer is conventionally known wherein a detecting lever of a microswitch is provided in a paper transport path such that it detects passage of paper in the paper transport path to turn the microswitch on and such detection signal of the microswitch is transmitted by way of signal lines. Another paper detecting apparatus is also known wherein a photo-sensor is provided across a paper transport path such that presence or absence of paper passing through the paper transport path is detected by the photo-sensor and such detection signal is transmitted by way of signal lines. A further paper detecting apparatus is also known which includes a mechanical mechanism which is constituted such that a paper detecting member is provided for pivotal motion in a paper transport path and such pivotal motion of the paper detecting member is converted by way of a shaft into pivotal motion of an arm while an end of the arm is detected by means of a photo-sensor.
While such conventional paper detecting apparatus individually have various advantages and disadvantages, they can be used without much trouble where the distance between the paper detecting section and the controlling section is comparatively small. However, where the distance between the paper detecting section and the controlling section is great, in the case of a paper detecting apparatus of the type wherein a detection signal from a microswitch or a photo-sensor is transmitted by way of signal lines, a soldering operation and so forth are required, which requires a high production cost. Besides, a countermeasure for preventing the detecting section from serving as a source of noises and a countermeasure for assuring a resisting property to static electricity and so forth are required, which involves a considerably high cost. Further, since a photo-sensor is comparatively expensive, where a plurality of paper transport paths for detecting passage of paper are involved, a very high cost is required because a photo-sensor must be provided for each of such paper transport paths.
Meanwhile, in the case of a paper detecting apparatus which includes a mechanical mechanism, if the distance between the paper detecting section and the photo-sensor increases, then the amount of movement of an end of the arm increases progressively, and accordingly, a great spacing is required in a printer in order to assure an area for movement of the arm. Accordingly, it is a disadvantage that the printer must have a correspondingly great overall size.